The idea for this project came from two separate project plans:
a) I've wanted to build battery powered, bluetooth speaker for small gatherings (less then 20 people),
b) I wanted to build my first MEH (multy entry horn).
So I almost started with two separate projects, but then I said to my self: "Hmmm, is it possible to combine both things into one project => to build relatively small, portable , battery powered MEH, so I could kill two flies with one blow?"
And then, after couple of months of reading MEH threads on this forum (and outside forum), I've narrowed down my design requirements:
1.) Weight=>when completed, the whole box should be easily grabbed & lifted with one hand,
2.) Size =>the box should be around 350 x 350 x 350mm (so around 45L gross volume),
2.) Sound output =>105db/1m will be sufficient, of course the more headroom the better, but in this particular case I would rather sacrifice output for sound quality,
3.) Frequency range => from 50Hz to 20kHz,
4.) Horn type => design should be based on off-the-shelf plastic horn, with added two woofers on the side and one full range on throat flange.
5.) Lower cut-off frequency => 500 Hz should be sufficient, as it dictates portability,
6.) Loudspeaker drivers selection => initial testing will be done with my existing drivers (two 6.5" woofers & one 2" full range driver).
If the initial concept will be promising, then I will invest into new (better) drivers.
7.) Box material => most probably I will use light 10mm plywood.
8.) Amplification & DSP=> the plan is to use plate amp with DSP , but that can run on batteries (something like "Arylic Up2Stream Plate Amp 2.1").
9.) Batteries & charger => to keep things light, I plan to use Li-Ion batteries, with dedicated battery charger.
When you search MEH threads on this forum, there are plenty interesting projects, and lot of them have similar features as my project, but I couldn't find any specifically built portable MEHs.
The first thing that I wanted to define was which CD horn to choose => so I browsed through catalogues of various manufacturers and in the end I chose "SB Acoustics" H280horn:
https://www.sbaudience.com/index.php/products/horns/horn-h280/
Few reasons:
a) It has 500Hz lower cut-of frequency,
b) The size of the horn is about maximum possible to fit in desired box,
c) It has nice, large, flat areas, for mounting two woofers,
d) The distance between horn mouth and horn throat , and horn cross section allows mounting of two 8" woofers.
a) I've wanted to build battery powered, bluetooth speaker for small gatherings (less then 20 people),
b) I wanted to build my first MEH (multy entry horn).
So I almost started with two separate projects, but then I said to my self: "Hmmm, is it possible to combine both things into one project => to build relatively small, portable , battery powered MEH, so I could kill two flies with one blow?"
And then, after couple of months of reading MEH threads on this forum (and outside forum), I've narrowed down my design requirements:
1.) Weight=>when completed, the whole box should be easily grabbed & lifted with one hand,
2.) Size =>the box should be around 350 x 350 x 350mm (so around 45L gross volume),
2.) Sound output =>105db/1m will be sufficient, of course the more headroom the better, but in this particular case I would rather sacrifice output for sound quality,
3.) Frequency range => from 50Hz to 20kHz,
4.) Horn type => design should be based on off-the-shelf plastic horn, with added two woofers on the side and one full range on throat flange.
5.) Lower cut-off frequency => 500 Hz should be sufficient, as it dictates portability,
6.) Loudspeaker drivers selection => initial testing will be done with my existing drivers (two 6.5" woofers & one 2" full range driver).
If the initial concept will be promising, then I will invest into new (better) drivers.
7.) Box material => most probably I will use light 10mm plywood.
8.) Amplification & DSP=> the plan is to use plate amp with DSP , but that can run on batteries (something like "Arylic Up2Stream Plate Amp 2.1").
9.) Batteries & charger => to keep things light, I plan to use Li-Ion batteries, with dedicated battery charger.
When you search MEH threads on this forum, there are plenty interesting projects, and lot of them have similar features as my project, but I couldn't find any specifically built portable MEHs.
The first thing that I wanted to define was which CD horn to choose => so I browsed through catalogues of various manufacturers and in the end I chose "SB Acoustics" H280horn:
https://www.sbaudience.com/index.php/products/horns/horn-h280/
Few reasons:
a) It has 500Hz lower cut-of frequency,
b) The size of the horn is about maximum possible to fit in desired box,
c) It has nice, large, flat areas, for mounting two woofers,
d) The distance between horn mouth and horn throat , and horn cross section allows mounting of two 8" woofers.
I purchased three pieces of "SB Acoustics" H280 horns:
a) One will be used only for testing/experimentation,
b) The other two will be used in actual design.
Please note that I have plan A and plan B for using two horns:
a) Plan "A" is to simply make two smaller boxes, one for left channel, and one for right channel , within above dimensions.
b) Plan "B" is to try combining both horns in one box, with two horns placed side by side, but with certain angle, to maximize coverage area, but to minimize interference (of course if such arrangement offers good sound),
That way, each horn will have two 8" woofers, and one 2.5" fullrange driver, so the whole box will have four 8" woofers and two 2.5" fullrange drivers.
Of course, this will increase overall volume of the box, and it will be a challenge to make such box light, but it should provide stronger sound output.
So, first job was to create 3D rendering of the H280 horn => I took some general dimensions from the "SB Acoustics" website drawings, and measured other features directly on physical horn.
Then, I've took my old car woofers (20-year old, "basement specials", poly cone, with little bit rusty frames, but still good rubber surrounds), and took their dimensions and created 3D model as well.
(NOTE: Unfortunately, I don't have T/S parameters for these drivers, but I was using them loooong time ago for my 2-way floorstanding speakers, and if I remember correctly run two of them in approx. 30L closed box, from 50Hz to approx. 3500Hz => I am guessing that Qts is around 0.6-0.7, resonant frequency is around 60Hz, and VAS could be around 14-15L cca.)
After making 3D model of the woofer I played with woofer position, taking into account all basic MEH rules:
a) To place woofer taps as close horn throat as possible,
b) To position woofer taps close to the corners of the horn,
c) To position woofer taps relatively close to woofer membrane center,
d) To make small, elongated slots for woofer taps, which I can enlarge if required,
e) To find position, for mounting woofer where woofer mounting plate will be easily glued/attached.
For fullrange driver, I didn't had any spare 2" or 2.5" drivers around, so I simply took one old PC speaker, took it apart, and took one driver from it => there are no marks on the driver, so I don't have any info about performance - but it is 2" diameter, which should enable simple mounting to horn throat , with simple throat adapter.
I've created model of this fullrange driver as well, plus mounting plate for this driver - and then combined all these 3D parts in one 3D assembly:
a) One will be used only for testing/experimentation,
b) The other two will be used in actual design.
Please note that I have plan A and plan B for using two horns:
a) Plan "A" is to simply make two smaller boxes, one for left channel, and one for right channel , within above dimensions.
b) Plan "B" is to try combining both horns in one box, with two horns placed side by side, but with certain angle, to maximize coverage area, but to minimize interference (of course if such arrangement offers good sound),
That way, each horn will have two 8" woofers, and one 2.5" fullrange driver, so the whole box will have four 8" woofers and two 2.5" fullrange drivers.
Of course, this will increase overall volume of the box, and it will be a challenge to make such box light, but it should provide stronger sound output.
So, first job was to create 3D rendering of the H280 horn => I took some general dimensions from the "SB Acoustics" website drawings, and measured other features directly on physical horn.
Then, I've took my old car woofers (20-year old, "basement specials", poly cone, with little bit rusty frames, but still good rubber surrounds), and took their dimensions and created 3D model as well.
(NOTE: Unfortunately, I don't have T/S parameters for these drivers, but I was using them loooong time ago for my 2-way floorstanding speakers, and if I remember correctly run two of them in approx. 30L closed box, from 50Hz to approx. 3500Hz => I am guessing that Qts is around 0.6-0.7, resonant frequency is around 60Hz, and VAS could be around 14-15L cca.)
After making 3D model of the woofer I played with woofer position, taking into account all basic MEH rules:
a) To place woofer taps as close horn throat as possible,
b) To position woofer taps close to the corners of the horn,
c) To position woofer taps relatively close to woofer membrane center,
d) To make small, elongated slots for woofer taps, which I can enlarge if required,
e) To find position, for mounting woofer where woofer mounting plate will be easily glued/attached.
For fullrange driver, I didn't had any spare 2" or 2.5" drivers around, so I simply took one old PC speaker, took it apart, and took one driver from it => there are no marks on the driver, so I don't have any info about performance - but it is 2" diameter, which should enable simple mounting to horn throat , with simple throat adapter.
I've created model of this fullrange driver as well, plus mounting plate for this driver - and then combined all these 3D parts in one 3D assembly:
Attachments
As this box will be test box, I decided to temporarily fix all plywood boards on the horn, so I can easily change them if required.
So instead epoxy (or some other strong) glue, I used doubly sticky tape (strong type).
With sufficient area, sticky tape can offer quite good holding force, so I applied tape to maximize surface:
So instead epoxy (or some other strong) glue, I used doubly sticky tape (strong type).
With sufficient area, sticky tape can offer quite good holding force, so I applied tape to maximize surface:
When all plywood board for woofer were cut down and temporarily glued to H280 horn, I carefully drilled elongated holes in plastic horn, by using plywood boards as guides.
Then, all holes were sanded smooth, and foam gasket was added on both 6.5" woofers.
Woofers were then attached to both boards, and wires were soldered.
For the fullrange driver board, I also used 18mm birch plywood => as the membrane diameter of my "no-name" driver was around 46mm, and H280 throat was 35.5 mm (1.4"), I decided for this test to simply make conical plywood adapter, without additional compression volume immediately in front of the driver.
Plywood adapter with fullrange driver was then attached to horn, and wires were soldered to driver.
As probably most guys here, I was anxious to hear the whole assembly in free air, without any box => I must admit, I didn't knew what to expect as I was not doing any software simulations/calculations, as I was stubborn, and was trying to see how "forgiving" such MEH design is in real life, if you stick to essential rules.
But on my surprise, sound was quite pleasant even with my 20-years old, rusty woofers and "no-name" fullrange speaker - short video clip is here:
Hm, even with small amount of DSP correction, with randomly chosen drivers, without any box, this MEH sounds very clean and well defined => I would say that it sound much better that it should deserve, considering lack of proper calculations/ simulations.
So, now I was obviously curious, how it would sound with some kind of box, any type of the box => the simplest box I could think of was actually standing right next to my leg => the cardboard box for the H280 horn
Therefore, by using some masking tape & sharp knife I quickly placed complete horn assembly into cardboard box => it was of course (too) tight fit, and undersized internal volume but for quick tests, who cares
Now, with horn placed in improvised cardboard box, I've gain some output in bass region, so I could easily reach 50Hz, or even a little bit lower, but of course this is still far from optimal as box volume is sub-optimal, lot of bass energy is absorbed in box itself, plus box is leaking somewhat.
The sound is still very good & balanced - especially the amount of details when you hear the box from the larger distance (5 to 10meters).
For example, this short video is taken in my office (which is acoustically, far from ideal listening room), with horn simply placed on chair, and from 10m distance (song: Nils Lofgren - Keith Don't Go):
Then, all holes were sanded smooth, and foam gasket was added on both 6.5" woofers.
Woofers were then attached to both boards, and wires were soldered.
For the fullrange driver board, I also used 18mm birch plywood => as the membrane diameter of my "no-name" driver was around 46mm, and H280 throat was 35.5 mm (1.4"), I decided for this test to simply make conical plywood adapter, without additional compression volume immediately in front of the driver.
Plywood adapter with fullrange driver was then attached to horn, and wires were soldered to driver.
As probably most guys here, I was anxious to hear the whole assembly in free air, without any box => I must admit, I didn't knew what to expect as I was not doing any software simulations/calculations, as I was stubborn, and was trying to see how "forgiving" such MEH design is in real life, if you stick to essential rules.
But on my surprise, sound was quite pleasant even with my 20-years old, rusty woofers and "no-name" fullrange speaker - short video clip is here:
Hm, even with small amount of DSP correction, with randomly chosen drivers, without any box, this MEH sounds very clean and well defined => I would say that it sound much better that it should deserve, considering lack of proper calculations/ simulations.
So, now I was obviously curious, how it would sound with some kind of box, any type of the box => the simplest box I could think of was actually standing right next to my leg => the cardboard box for the H280 horn
Therefore, by using some masking tape & sharp knife I quickly placed complete horn assembly into cardboard box => it was of course (too) tight fit, and undersized internal volume but for quick tests, who cares
Now, with horn placed in improvised cardboard box, I've gain some output in bass region, so I could easily reach 50Hz, or even a little bit lower, but of course this is still far from optimal as box volume is sub-optimal, lot of bass energy is absorbed in box itself, plus box is leaking somewhat.
The sound is still very good & balanced - especially the amount of details when you hear the box from the larger distance (5 to 10meters).
For example, this short video is taken in my office (which is acoustically, far from ideal listening room), with horn simply placed on chair, and from 10m distance (song: Nils Lofgren - Keith Don't Go):